if present tense + subject would/will.
Examples - a. If Mary tells you the details of her job, she would be failing in her duties.--v--b. If Mary tells you the details of her job, she will be failing in her duties.
Q. I have seen this sort of pairing (present tense in the if-clause and "would in the main clause) before. I'd like to know if a is correct, and if so, how it differs from b.
A. Yes, "a." is correct as "would" is used as a conditional verb.
Would is a past tense form of will. It is also a conditional verb that indicates an action that would happen under certain conditions.
Conditional verbs are used to create conditional sentences, which express hypothetical or unlikely situations. Conditional verbs can be used in the past, present, or future tense, and auxiliary verbs like can/could, will/would, and may/might are important in forming conditionals.
If I had enough money, I would travel around the world. Ref Grammarly
"b." is incorrect in this case; as a modal verb is usually followed by the root form of a verb. If we rewrite "b.2 If Mary tells you the details of her job, she will fail in her duties. The sentence now has a different meaning or implication may be a better way to explain it. The use of will now indicates something in the far future. If it was to happen in the "near" future we would not use "will" but "going to" Expressing a Future Action: When To Use “Will” And “Going To”.
For b. to be correct we would have to write
If Mary tells you the details of her job, she is "going to" be failing in her duties.
Will can be a present tense verb that means to cause something to happen through force of desire. It can also be a modal auxiliary verb in various tenses.
USE WILL FOR A FAR FURTHER FUTURE ACTION
One important detail about “WILL” is that it is most often used to discuss things or situations that may take a long time to happen.
WHEN TO USE “GOING TO”
One huge difference in using GOING TO versus WILL, is that you use GOING TO when the action was already decided on even before speaking of it.